This October we will be finishing a cruise in Piraeus and would like to rent a car to visit Napflio and Meteora before leaving to fly home from Athens. We will have already visited Athens, Delphi and Olympia on a tour before the cruise. Should we take a cab back to the airport to rent a car? Should we book a day monastery tour from Kalambaka? Would it be possible to squeeze in a visit to Ioannina on the way to Kalambaka? We have a week. I would love some further ideas or insight. Many thanks.
You could probably pick up at Piraeus and drop off at airport with no to minimal charge. I would compare that to pick up/drop off at airport, including the charge for the Piraeus to airport transfer/transport.
I had a plan to visit Meteora before covid that got nixed, so I am not sure if a tour is needed or not. I planned to do it independently, but I'm a big walker. I found drive times fairly accurate on Google Maps for my Peloponnese trip, so I would suggest first working out how much you want to drive each day, then sort out how many days for each place and the order.
Nafplio is about two hours from ATH, so if your outbound flight is late afternoon or later, you could even stay there before departure without having to stay near airport or return to Athens for last night. Of course many other options for that last night as well. You could spend a full week in Nafplio and easily have more left to see in the area when you leave, so it just depends on your wish list. I personally would make northern Greece a separate trip, but if you have your heart set on both this trip, it is definitely doable. Again, look at drive times and make a proposed itinerary to see what works for you. If you do decide to save Meteora, there are some stunning (though less extensive) monasteries in the Peloponnese (at Stemnitsa).
You can pick up a car at the port of Piraeus and return it to the airport or to the city center.
Several rental agencies are located at the port of Piraeus.
For example Capital Rent A Car has offices in Piraeus, Athens city center and airport. (and in Thessaloniki)
They will wait for you with the car at the dock when the ferry or cruise ship arrives